Diesel engines convert chemical energy from a fuel into mechanical energy. The fuel usually is petroleum-based. Most diesel engines compress air in a cylinder and then inject fuel into the cylinder for the compressed air to ignite. The ignited fuel generates rapidly expanding gases that actuate a piston in the cylinder. The piston usually is connected to a crankshaft or similar device for converting the reciprocating motion of the piston into rotational motion. The rotational motion from the crankshaft may be used to propel a vehicle, operate a pump or an electrical generator, or perform other work. The vehicle may be a truck, an automobile, a boat, or the like.
Many diesel engines have an exhaust gas recirculation (EGR) system to reduce the production of nitrogen oxides (NOX) during the combustion process in the cylinders. The EGR system typically diverts a portion of the exhaust gases for mixing with air entering the engine for combustion. The exhaust gases generally lower the combustion temperature below the temperature where nitrogen combines with oxygen to form nitrogen oxides (NOX).
To divert the exhaust gases, most EGR systems connect to the exhaust manifold of the engine. The exhaust manifold generally is an accumulation chamber above the cylinders that gathers the exhaust gases for expulsion from the vehicle. Many EGR systems have a pipe or other conduit that connects to the exhaust manifold. The pipe may divert the exhaust gases through a gas cooling device such as a heat exchanger prior to mixing the exhaust gases with the incoming air to the cylinders. The exhaust gases may have a temperature in the range of about 300° F. (149° C.) through about 1,500° F. (815° C.) during engine operation.
In many EGR systems, the pipe or other conduit is connected to the exhaust manifold by bolting a flat connection surface on the pipe against a flat connection surface on the exhaust manifold. A gasket usually is placed between the connection surfaces. The flat connection may increase the assembly time and costs due to the dimensional variations of the pipe and other components in the EGR system. The flat connection may distort and leak from the higher temperatures, thermal cycling, and thermal expansion at the connection with the exhaust manifold.
Some EGR systems use a pipe with a flexible element to reduce the assembly variation and thermal expansion from the connection with the exhaust manifold. The flexible element may increase the costs of the EGR system and may leak and fail from the higher temperatures and thermal cycling of the connection with the exhaust manifold.